A continuous descent approach is an approach that does not include level flight sections such as those present in conventional approaches. This approach in particular makes it possible to simplify the separation of different aircraft into different flows. This approach is made by making the aircraft comply with two constraints. The first constraint that the aircraft must comply with is the angle of the flight plane, also known by the English acronym FPA (Flight Path Angle). This angle is generally included between −2° and −3°. The second constraint that the aircraft must comply with is the speed with respect to the ground. However, the aircraft cannot directly know its speed with respect to the ground. In fact the aircraft can only know its speed with respect to the surrounding mass of air (this speed is also known by the expression “indicated speed” or by the English acronym IAS (Indicated Air Speed)). Via equipments external to the aircraft, it can also know the speed of the surrounding mass or air, or wind speed. By using these two speeds, the systems of the aircraft can determine the speed of the aircraft with respect to the ground.
This approach is conventionally managed by the fight management system, also known by the English acronym FMS (Flight Management System). In order to control its trajectory, the flight management system acts on the position of the flaps, slats, airbrakes and undercarriages. Some of these items can assume several positions, which is the case for the flaps and the slats. The airbrakes can assume several discrete positions (generally “retracted”, “deployed” and “50% deployed”, but some aircraft can have intermediate settings like 25% and 75%). The undercarriages can only assume two positions, a retracted position and a deployed position. The expression aerodynamic configuration is used to denote a configuration of the positions of these various elements. The flight management system also acts on the speed of the different engines.
For some types of flight, like for example the CDA approaches, the start and end points of the transitions between the different configurations cannot be calculated in the same way as for a conventional descent. Similarly, the impact of the transitions on the end time of the flight cannot be calculated in the conventional way.
The U.S. Pat. No. 7,611,098 and U.S. Pat. No. 8,027,758 propose a method for calculating the end time of the CDA procedure by taking account of the different configurations of the aircraft during the descent. However, these two patents do not take account of the dynamics associated with these different transitions. Thus, in these patents, the flaps are considered as having a distinct and finite number of positions and the effect of the transition on the trajectory of the aircraft is not taken into account. Moreover, these patents do not present the determination of the start and end points of the different transitions between aerodynamic configurations nor the impact of these transitions on the end time of the flight.
The patent application EP 2551836 presents a method taking into account the dynamics of transition between the different aerodynamic configurations; however, this patent application presents this taking into account in order to optimize the management of the energy of the aircraft and not to determine the start and end points of the different transitions between the aerodynamic configurations or the impact of these transitions on the end time of the flight.